The present invention relates to a telecommunication system comprising a linecard with at least one ISDN basic access interface for coupling the telecommunication device to at least one ISDN supported device or to an ISDN network via a four-wire transmission line.
The present invention further relates to a linecard for use in such a telecommunication device.
A telecommunication system of this kind is known from an article "Communication system for the parliament of Northrhine-Westfalia (Landtag NRW)", H. Friedel, J. Wiegand, Philips TDS Review, Vol. 46, No. 1, March 1988, pp. 1-13. In this article an ISDN-compatible (Integrated Services Digital Network) PABX (Private Automatic Branch Exchange) is disclosed with stored-program control and digital switching, which can be used both in analog and digital switching, its capacity ranging from 200-20,000 extensions. The digital communication is based on a procedure recommended by the CCITT, an ISDN Basic Rate Access 2B+D, two B-channels for user information, 2 times 64 kbit/s digital speech and data, and one D-channel for signalling or user data, 16 kbit/s, with a netto rate of 144 kbit/s and a bruto rate of 192 kbit/s, and an ISDN Primary Rate Access 30B+D, with a rate of 2048 kbit/s. Physically, the 2B+D and 30B+D form a single link, i.e. the 2B+D and 30B+D channels are multiplexed, but logically, from a user point of view, these channels are totally independent of each other. The PABX communicates with ISDN telephone sets, PCs etc. via ISDN basic access interfaces at 192 kbit/s (Basic Rate Access), and may communicate at the higher 2048 kbit/s with larger computer systems, with other PABXs, with the public ISDN etc. The PABX may also communicate with other PABXs or the public ISDN at Basic Rate. Communication can be point-to-point or point-to-multipoint, possibly via a LAN (Local Area Network). The PABX may also comprise analog interfaces for communicating with the PSTN or with analog telephone sets via a Terminal Adapter, adapting analog devices to an ISDN interface. The basic access interface has the following OSI-model layer 1 characteristics: four-wire transmission line with phantom power feeding, 192 kbit/s (2B+D, contention resolution, and transmission overhead), point-to-point or multipoint/passive S.sub.o -bus, AMI (Alternate Mark Inversion) or ternary line code.
Further details concerning ISDN and ISDN user-network interfaces can be found in the CCITT `Blue Book`, Vol. III-Fascicle III-8, Recommendations I.310-I.470, CCITT IXth Plenary Assembly, Melbourne, 14-25 Nov. 1988, issued Geneva 1989, particularly pp. Rec. I.410, pp. 155-156, Rec. I.411, pp. 157-163, Rec. I.412, pp. 163-168, Rec. I.421, pp. 169, I.430, pp. 204-209. In Rec. I.411 reference configurations for ISDN user-network interfaces are given, in terms of TE1 (ISDN Terminal Equipment), TE2 (non-ISDN Terminal Equipment), NT1 (Network Termination 1), NT2 (Network Termination 2), and further so-called S-, T- and U-reference points. NT1, which interfaces to a transmission line is broadly equivalent to layer 1 of the OSI layer model, and NT2, is broadly equivalent to layers 1 to 3 of the OSI model. PABXs, LANs, and terminal controllers are examples of equipment or combinations of equipment that provide NT2 functions.. It will be assumed in the sequel that an NT will include NT2 and NT1, and that TE implies TE1. In Rec. I.430, at pp. 204-205, a reference configuration for phantom power feeding is described for the basic access interface at the S-reference point. In FIG. 20/I.430 at page 205, a four-wire transmission line is shown connected an NT to a TE, at the NT transmitter side power being feeded to the transmission line at a phantom power point of a line transformer to which further data to be transmitted is fed, and at the NT receiver side ground being connected to a line transformer for receiving data.
In the International application WO 89/11189 a D-channel ISDN-monitor is described which is capable of providing a plurality of operating modes for monitoring of D-channel operation. For being able to monitor both NTs and TEs, the D-channel monitor is provided with ISDN basic interfaces or S-interfaces of Intel type iATC 29C53AA Digital Loop Controller, which is a 4-wire transceiver/controller that is CCITT I.430 compatible and can function at either loop end, i.e. it can be used in linecard (NT) applications or in voice/data subscriber (TE) applications. In the disclosed D-channel ISDN-monitor such a programmable Digital Loop Controller is used to simulate an NT or a TE, both for monitoring purposes only.
Telecommunication devices such as PABXs usually comprise a number of analog or digital linecards and have to fulfill customer specific demands, i.e. one customer may require a quite different PABX configuration than another customer, because of the fact that differents sets of devices have to be coupled to the PABX. As regards the digital linecards, which usually comprise a number of ISDN basic access interfaces, this might imply that a great many of customer specific linecards would have to designed and manufactured, bringing along high manufacturing change-over costs, expensive and extra documentation to be supplied etc.